This invention relates to a method of non-contact transmission of measured values and a respective arrangement for non-contact transmission of measured values.
Methods or arrangements for non-contact transmission are preferably used for measured values from measuring units which are not easily accessible and whose measured values are not required continuously. Examples of this category are many measurements of consumption data and temperature measurements such as the measurement of a room temperature for controlling a heating system. Also in the medical field, when physiological measured values of an implanted measuring unit are necessary, over a rather long period of time, such methods or arrangements can be used to advantage.
From WO 95/27272 is known a method and apparatus by which measured values of a remote measuring unit can be read by a reading device. At the measuring unit there are a sensor and an electronic interface unit, which interface unit is powered by a local power source and converts the measured values of the sensor into preferably digital measured data. Furthermore, both the measuring unit and the reading device have a transceiver arrangement. In order to have the least possible power consumption of the power source, the interface unit is rendered inactive during rather long periods of time and switched to the receiving mode only periodically. When data are to be transmitted, the reading device transmits a data request signal, recurrently if need be, until a request signal occurs during the period of time in which the interface unit is in the active state. This interface unit then causes a measured value or a sequence of measured values to be transmitted. This data transmission requires relatively much power from the power source even though this is for a brief period of time, so that the power source is heavily loaded and has a short useful life when measured data are transmitted frequently.
From EP 0 601 739 A2 is known a data transmission method of a measuring unit by means of an interrogation circuit, in which the circuit of the measuring unit and the interrogation circuit are coupled to each other via antennas. The power for operating the sensor and converting the measured values and transmitting them is provided via these antennas. The measuring unit thus does not need a power source of its own. However, a measurement can only be effected if the interface unit is in the active state. In addition, an interface unit is capable of reaching no more than one measuring unit in this manner. On the other hand, with this known method it is not possible that data can no longer be measured or transmitted due to the premature running down of the power source, because the interrogation circuit is easily accessible or stationary, and can therefore have sufficiently large power reserves.